In current biological treatment processes, suspended solids need to be removed from effluent before it flows to a next treatment unit or a receiving water body. In general, after wastewater is subjected to an aerobic treatment process to remove suspended solids, a five-day Carbonaceous Biochemical Oxygen Demand (CBOD5) test of a resultant effluent usually meets regulatory discharge limits. Thus, removing suspended solids from effluent is a key point in an aerobic treatment system.
In most municipal sewage treatment plants, a surface skimmer is used to remove surface sludge and a bottom scraper is used to remove settled sludge in a sedimentation tank or unit. The supernatant from the sedimentation tank can then be directed to a next treatment unit or discharged to a receiving water body. However, in residential sewage treatment plants, daily, weekly, and monthly maintenance services are not economically practical. Instead, these types of maintenance services only can be offered after a certain operational period of time. Therefore, the plant frequently must be operated without maintenance services during this period of time except to fix mechanical or electrical problems. Therefore, because the surface skimmer and sludge scraper are not practical for use in a residential sewage treatment plant or system, what is needed is a residential treatment plant that can remove the suspended solids from the effluent without the use of the surface skimmer and/or the bottom sludge scraper.